Exhaust gas purification filter

Abstract

Provided is an exhaust gas purification filter including a substrate comprising a plurality of porous partitions, wherein the partitions form an exhaust gas flow path, a porous catalytic layer is provided on the partitions and the catalytic layer having a thickness of 10 μm or greater is provided over at least 20% of the total length of the partitions in the lengthwise direction thereof, and the catalytic layer having a thickness of 10 μm or greater is not present on the partitions 15 mm from an outflow side.

The invention claimed is: 
     
       1. An exhaust gas purification filter comprising a substrate comprising:
 a plurality of porous partitions, wherein the partitions form an exhaust gas flow path, wherein an on-wall porous catalytic layer comprising a catalyst component is provided on the partitions, the catalytic layer having a thickness of between 10 μm and 50 μm, wherein the mean diameter of pores in the catalytic layer is between 1 and 5 μm, the void ratio of the catalytic layer is no greater than 50%, the catalyst component is present in the layer at a loading of 10 to 40 g/L, and the catalytic layer is present-over at least 20% of the total length of the partitions in the lengthwise direction thereof, and 
 the catalytic layer having a thickness of between 10 μm and 50 μm is not present on the gas inflow-side partitions within 15 mm from an outflow side of the filter. 
 
     
     
       2. The exhaust gas purification filter according to  claim 1 , wherein the application amount of catalyst component forming part of the catalytic layer varies according to the specific gravity of the catalyst component and the pore volume in the catalytic layer. 
     
     
       3. The exhaust gas purification filter according to  claim 1 , wherein the mean diameter of the pores in the catalytic layer is between 2 and 5 μm. 
     
     
       4. The exhaust gas purification filter according to  claim 1 , wherein the void ratio of the catalytic layer is between 30 and 50%. 
     
     
       5. The exhaust gas purification filter according to  claim 1 , wherein the void ratio of the partitions is between 40% and 60%. 
     
     
       6. The exhaust gas purification filter according to  claim 1 , wherein the mean diameter of the pores in the partitions is between 10 μm and 20 μm. 
     
     
       7. The exhaust gas purification filter according to  claim 1 , wherein the catalyst component comprises at least one of platinum and palladium, and at least one of an alkali metal and a rare earth metal. 
     
     
       8. The exhaust gas purification filter according to  claim 1 , wherein the thickness of the catalytic layer is between 10 μm and 20 μm. 
     
     
       9. The exhaust gas purification filter according to  claim 1 , wherein the catalytic layer covers at least 50% (excluding 15 mm from the outlet) of the total length of the partitions in the lengthwise direction from the inlet. 
     
     
       10. The exhaust gas purification filter according to  claim 1 , wherein the catalytic layer covers less than 50% (excluding 15 mm from the outlet) of the total length of the partitions in the lengthwise direction from the inlet. 
     
     
       11. A method for producing an exhaust gas purification filter according to  claim 1 , the method comprising:
 (a) applying a slurry comprising a catalyst component and an organic pore-forming material to a support 
 (b) forming pores in a catalytic layer; wherein the organic pore-forming material is a combustible material having a specific gravity at the same level as that of a slurry aqueous solution and particle size of the pore-forming material is between 1 and 5 μm, and 
 (c) providing voids in the catalytic layer. 
 
     
     
       12. The method for producing an exhaust gas purification filter according to  claim 11 , wherein the mean length/diameter ratio of the organic pore-forming material is 1.5 or less. 
     
     
       13. The method for producing an exhaust gas purification filter according to  claim 11 , wherein the step of providing voids in the catalytic layer is formed by heating the support comprising the slurry comprising a catalyst component and an organic pore-forming material to a support to decompose or combust the organic pore forming material.